JP2000271988A - Manufacture of aliphatic polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film uniform in thickness efficiently, continuously and stably by imparting proper viscosity to an extruded melt while preventing the generation of a stain. SOLUTION: In a aliphatic polyester film manufacturing method wherein a melting component based on aliphatic polyester having a main repeating unit represented by general formula -O-CH-R-CO (wherein R is H or a 1-3C alkyl group) is melted to be extruded and the obtained extruded melt is brought into close contact with a rotary cooling roll to be taken over while quenched and solidified to obtain an unstretched film, polyester to be used has a melt viscosity of 1×103-below 1×106 poise at 200 deg.C under a shearing speed condition of 10/sec and melt extrusion is performed within a temp. range from the melting temp. (Tm) of aliphatic polyester to 250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aliphatic polyester film, which is obtained by melt-extrusion and then quenched and solidified by a rotary cooling roll to obtain an unstretched film. The aliphatic polyester film obtained by the present invention is used for various uses such as a film for packaging.

[0002]

2. Description of the Related Art Hitherto, films using an aliphatic polyester such as polylactic acid have been developed so as to be decomposed when discarded in a natural environment. For example, a polylactic acid film becomes a harmless degradation product by microorganisms after being naturally hydrolyzed in soil. In recent years, attention has been paid to the development of applications as general-purpose films, and development is being promoted (Japanese Patent Laid-Open No. 10-11945).
No. 3).

[0003] Generally, a biaxially stretched film is produced by stretching an unstretched film produced by a melt extrusion method such as an inflation method or a T-die method.
At that time, the extruded melt extruded by the T-die method is cast on a rotary cooling roll and solidified to form an unstretched film. At this time, as a means for bringing the extruded melt into close contact with the rotary cooling roll, a method of blowing air with an air knife (hereinafter referred to as an air knife method) or a method of depositing (charging) a charge on the melt from a high-voltage electrode to generate static electricity For example, a method of contacting by force (hereinafter, referred to as an electrostatic contact method) is used. This electrostatic adhesion method is described in, for example,
Japanese Patent Application Laid-Open No. 7-6142 discloses that since an extruded melt is tightly adhered to a rotating cooling roll and rapidly cooled by electrostatic force, a thermoplastic resin film can be produced efficiently and continuously stably. Has been described.

[0004]

However, when a film is produced using an aliphatic polyester, thermal decomposition is apt to occur during melting, so that the temperature range of melt extrusion is limited, and at the same time, an appropriate viscosity is obtained at that temperature. It was found that those having no film had poor film surface and thickness uniformity.

[0005] In other words, aliphatic polyesters have a higher rate of thermal decomposition at the time of melting retention at a temperature lower than the thermal decomposition start temperature than aromatic polyesters represented by polyethylene terephthalate and the like. And the range of residence time is very narrow. Therefore, if melt extrusion is performed under conditions outside this range, the degradation of the resin due to thermal decomposition becomes remarkable, a low molecular weight component is generated, and a part of the resin is gasified in the vicinity of the die, and bubbles and outflow and adhesion of degraded products Dirtyness occurs due to the above. As a result, in the electrostatic adhesion method, poor adhesion due to electrode contamination occurs, and contamination of the rotating cooling roll surface makes the adhesion and the cast state unstable, so that a series of steps can be continuously and stably performed. It became difficult, and problems such as uneven thickness in the film after biaxial stretching became apparent. On the other hand, even when the extrusion temperature is set in an appropriate range, if the extrusion melt does not have an appropriate viscosity,
Due to the entrainment of air and the fluctuation of the film surface of the extruded melt, the film surface and thickness became non-uniform.

Accordingly, an object of the present invention is to provide an extruded melt with an appropriate viscosity while preventing the generation of dirt.
An object of the present invention is to provide a method for producing an aliphatic polyester film, which can efficiently and continuously stably obtain a film having a uniform thickness.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, using an aliphatic polyester having a predetermined melt viscosity under a specific condition, at a predetermined temperature. It has been found that the above objects can be achieved by melt extrusion, and the present invention has been completed.

That is, the present invention provides a molten polyester containing an aliphatic polyester whose main repeating unit is a general formula -O-CHR-CO- (R is H or an alkyl group having 1 to 3 carbon atoms). The method for producing an aliphatic polyester film, which comprises a step of obtaining an unstretched film by melt-extruding the components and bringing the extruded extruded material into close contact with a rotary cooling roll and rapidly cooling and solidifying to obtain an unstretched film, The melt viscosity under the condition of a shear rate of 10 / sec at 200 ° C. is 1 × 1
A material having a melting point of at least ³ poise and less than 1 × 10 ⁶ poise is used, and the melt extrusion is performed within the melting temperature (Tm) of the aliphatic polyester to 250 ° C.

In the above, the close contact with the rotating cooling roll can be performed by an air knife method or the like, but the extruded melt is charged while being electrostatically attached to the rotating cooling roll (static). (Electro-contact method).

[0010] The aliphatic polyester includes various types as described below, and is preferably polylactic acid.

It is preferable that the method further includes a step of further stretching the unstretched film.

[Effects] According to the present invention, as shown in the results of the examples, the extruded melt is given an appropriate viscosity while preventing the occurrence of dirt, so that it can be efficiently and continuously stabilized. Thus, an aliphatic polyester film having a uniform thickness can be obtained. In other words, an aliphatic polyester having a predetermined melt viscosity under specific conditions is used, and melt extrusion is performed at a temperature at which a low molecular weight compound is not easily generated, so that melt extrusion with an appropriate viscosity becomes possible, and as a result, it is derived. It is possible to efficiently and continuously stably produce a film having a uniform thickness while solving the problem.

When the contact with the rotary cooling roll is performed by the electrostatic contact method as described above, the adhesive force to the rotary cooling roll is strong and the stability is high. Also,
In the electrostatic contact method, contamination of an electrode or the like used for charging tends to be a problem. In the present invention, the generation of a low molecular weight compound can be efficiently prevented as described above, so that the present invention is particularly effective. .

[0014] Among the aliphatic polyesters, polylactic acid is preferably used in the present invention from the comprehensive aspects such as moldability, heat resistance and cost.

In the case where the unstretched film is further stretched, a suitable melt extrusion is carried out as described above when obtaining the unstretched film. Good uniformity of thickness is obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The general formula -O-CHR-CO used in the present invention
The aliphatic polyester having-(R is H or an alkyl group having 1 to 3 carbon atoms) as a main repeating unit is, for example, a polymer of α-oxyacid such as polylactic acid, polyglycolic acid and poly (2-oxybutyric acid). Although coalescence can be mentioned, it is not limited to these. The aliphatic polyester may be used alone, or a mixture or a copolymer thereof may be used. The monomer having an asymmetric carbon such as α-oxy acid constituting the aliphatic polyester may be an optical isomer of L-form, DL-form or D-form, or may be a mixture of these isomers. . These aliphatic polyesters can be produced by a known method such as a method of ring-opening polymerization of a corresponding dehydrated cyclic ester compound such as α-oxy acid.

The aliphatic polyester preferably has a weight average molecular weight of usually about 10,000 to 500,000. When it is less than 10,000, the film obtained by being rapidly adhered to the rotating cooling roll becomes brittle and the physical properties are remarkably poor.
Also, there is a tendency for breakage to occur frequently in the subsequent biaxial stretching step. The weight average molecular weight is preferably 10,000 or more in order to ensure sufficient extrudability during molding and, for example, sufficient stretch moldability with a uniaxial or biaxial stretching machine. Considering these, the weight average molecular weight is preferably set to 20,000 or more. On the other hand, when the polymer has a weight average molecular weight of more than 500,000, it is difficult to obtain the polymer having the above-mentioned predetermined melt viscosity, and it becomes difficult to perform melt extrusion, so that the extrusion temperature tends to be increased. In consideration of these, the weight average molecular weight is preferably set to 400,000 or less.

The aliphatic polyester of the present invention has a temperature of 200 ° C.
And the melt viscosity under the condition of a shear rate of 10 / sec is 1 ×
Those having 10 ³ poise or more and less than 1 × 10 ⁶ poise are used. If the melt viscosity is lower than 1 × 10 ³ poise,
When the extruded melt is brought into close contact with the rotating cooling roll, the melt tension applied to the extruded melt is reduced, and air flowing as an entrained flow is caught between the rotating cooling roll and the extruded melt, and the surface and thickness uniformity are reduced. A good unstretched film cannot be obtained. Also, when air is blown by the air knife method, the flow of the air tends to cause the extruded melt to oscillate, and an unstretched film having a uniform thickness cannot be obtained. On the other hand, if the melt viscosity is 1 × 10 ⁶ poise or more, melt extrusion becomes difficult, and as a result, the extrusion temperature must be increased, and the resin is degraded due to thermal decomposition and the low molecular weight compound in the molten resin is reduced. The occurrence of the occurrence becomes severe, and a stable state of close contact with the rotating cooling roll cannot be continuously obtained.

In the present invention, in addition to the aliphatic polyester, generally used thermoplastic resins, rubbers, inorganic fillers, antioxidants, nucleating agents, etc. Plasticizers, compatibilizers, colorants,
An antistatic agent, a lubricant and the like can be added.

The production method of the present invention is a step of obtaining an unstretched film by melt-extruding the above-mentioned molten components, bringing the extruded extruded product into close contact with a rotary cooling roll, and rapidly solidifying the same to take it out. It has. The melt extrusion and quenching and solidification of such a molten component are performed by a known T
-It is performed by using a rotating cooling roll in the die method. Specifically, using a T-die (flat film die) or the like attached to the tip of the extruder, which extrudes the film raw material with various screws while heating and melting the film material,
While being extruded into a film, it is brought into close contact with a rotating cooling roll to be rapidly cooled and solidified, and then taken out by an appropriate means to obtain an unstretched film.

At this time, the temperature of the melt extrusion is in the range of the melting temperature (Tm) of the aliphatic polyester to be used to 250 ° C. If it is lower than Tm, it is difficult to obtain extrusion stability, and it is easy to fall into overload. On the other hand, when the temperature is higher than 250 ° C., the polymer is greatly decomposed and stains are generated, and it is difficult to continuously and stably perform a series of steps due to poor adhesion and instability of a cast state. From such a viewpoint, the temperature is preferably in the range of Tm + 10 ° C to 240 ° C.

As the die of the extruder used in the present invention, any of various types of T-die can be used.
The die temperature can be as high as the extrusion temperature range. During the extrusion process, a quantification pump, a filtration device, or the like may be used. These molding methods and molding apparatuses are known per se and are widely used.

The method of bringing the melt extrudate into close contact with the rotary cooling roll and rapidly cooling and solidifying it is not particularly limited, and may be any of an electrostatic adhesion method and an air knife method. However, from the above-mentioned reason, it is preferable to employ an electrostatic adhesion method in which the extruded melt is charged and electrostatically adhered to the rotary cooling roll while being charged. In that case, the electrode used for charging may be any of a wire electrode, a blade electrode, and a needle electrode.
The DC voltage applied from the electrodes is about 5 to 15 Kv, and the rotating cooling rolls form the electrodes to be paired. Note that an electrostatic adhesion method may be applied by forming a water film or the like on the surface of the rotating cooling roll.

The surface of the rotating chill roll may be metallic or non-metallic. When the electrostatic contact method is employed, a conductive material is preferred from the viewpoint of enhancing the adhesion due to static electricity. The surface temperature of the rotating cooling roll is usually 0 ° C.
To 60 ° C, preferably 10 ° C to 40 ° C, more preferably 20 ° C to 40 ° C. When the surface temperature of the rotary cooling roll is lower than 0 ° C., the adhesiveness between the end of the molten extrudate and the rotary cooling roll deteriorates, and the flatness of the obtained unstretched film deteriorates. On the other hand, when the temperature of the rotating cooling roll is 60 ° C.
If it exceeds 300, the adhesiveness between the melt extrudate and the rotary cooling roll will be too large, and it will be difficult to peel off the obtained unstretched film.

The unstretched film quenched and solidified in the rotating cooling roll is rotated at a speed corresponding to the rotating cooling roll speed.
It is picked up by a suitable means such as a winding device. At that time, the rotating cooling roll speed is usually 1 to 100 m / min.

Further, following the production method of the present invention, the obtained unstretched film may be subjected to various known uniaxial stretching steps or biaxial stretching steps to obtain various stretched films. In the case of performing biaxial stretching, stretching of the first axis and stretching of the second axis may be performed sequentially or simultaneously, and each stretching may be performed in one stage or in multiple stages.

[0028]

EXAMPLES Hereinafter, the contents and effects of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples unless departing from the gist thereof. The methods for evaluating physical properties in the following examples and comparative examples are as follows.

(1) Thickness unevenness Using a film thickness continuous measuring device manufactured by Anritsu Corporation, a thickness of 3 m was measured in the longitudinal direction of the film after biaxial stretching.
The thickness unevenness was calculated from the following equation.

Thickness unevenness = (maximum thickness−minimum thickness) / average thickness × 100 (%) (2) Melt viscosity 10 / sec at a shear rate using a Koka flow tester manufactured by Toyo Seiki Co., Ltd. The orifice diameter, orifice length, and load were selected so that the front and rear ranges could be measured, and the measurement was performed at 200 ° C.

(3) Degree of Staining The film forming operation of the biaxially stretched film was continuously performed for one hour, including the casting operation of melt-extruding the aliphatic polyester to obtain an unstretched film, and the area around the electrode at that time was carried out. The degree of coagulation of a low molecular weight product on the surface of the rotating cooling roll and the state of adhesion of the extruded melt to the surface of the rotating cooling roll were visually determined.

Example 1 The melt viscosity at a weight average molecular weight of 83,000 at 200 ° C. and a shear rate of 10 / sec was 2.3 × 10 ^4.
With respect to 100 parts by weight of Poise's poly-L-lactic acid, a molten component obtained by adding 0.06 parts by weight of aggregated silica particles having an average particle diameter of 1.8 μm as a lubricant for forming surface protrusions was used.
The melt extruded at a melt component temperature of 210 ° C. using a 30 mm diameter extruder with a T-die is heated at 30 ° C. with an air knife.
To obtain an unstretched film having a thickness of 300 μm. The speed of the rotating cooling roll was 8 m / min.

The unstretched film is heated by a roll heated to 75 ° C., stretched 3.5 times in the longitudinal direction, preheated to 60 ° C. in a tenter, and heated in the width direction while being heated from 70 ° C. to 75 ° C. Stretched 3.8 times, heat-set at 155 ° C,
The film was relaxed by 5% in the width direction at a temperature of 5 ° C. and subjected to a transverse relaxation treatment to obtain a biaxially stretched poly-L-lactic acid film having a thickness of 20 μm. This film forming operation was continuously performed for one hour, and the state of the subsequent film formation was observed.

After one hour, a faint
Adhesion of a low molecular weight product was observed, but no particular change was observed in the state of adhesion of the extruded melt to the rotating cooling roll. The thickness unevenness of the obtained biaxially stretched film was 12%.

Example 2 Example 2 was carried out in the same manner as in Example 1 except that an unstretched film was produced by an electrostatic adhesion method instead of the air knife method. As the electrostatic contact method, a tungsten wire electrode is provided between a die and a rotary cooling roll, and a DC voltage is applied from the electrode to a molten film extruded from a T-die at a temperature of 210 ° C. by applying a DC voltage of 5 Kv to 15 K.
v was applied to make it adhere to a 30 ° C. rotating cooling roll.

After 1 hour, no adhesion of a low molecular weight substance was found on the rotating cooling roll. Also, no particular change was observed in the state of adhesion of the extruded melt to the rotary cooling roll. The thickness unevenness of the obtained biaxially stretched film was 8
%Met.

Comparative Example 1 The procedure of Example 1 was repeated, except that poly-L-lactic acid having a weight average molecular weight of 43,000 was used. The melt viscosity at 200 ° C. at a shear rate of 10 / sec was 820 poise.

After one hour, the state of adhesion of the extruded melt to the rotary cooling roll was not stable. Further, the obtained biaxially stretched film had poor thickness unevenness, and frequently fractured during the formation of the biaxially stretched film.

Comparative Example 2 In Example 2, poly-L-lactic acid having a weight average molecular weight of 550,000, a melt viscosity at 200 ° C. and a shear rate of 10 / sec at 1.2 × 10 ⁶ poise was used. Except for the above, all the processes were performed in the same manner as in Example 1. However, in the melt extrusion at 210 ° C., the back pressure was high and the extrusion was difficult. For this reason, the temperature setting of the melt extrusion was set to 260 ° C. Otherwise, the procedure was the same as in Example 1.

After one hour, a large amount of low molecular weight substances were found to adhere on the rotating cooling roll. In addition, low molecular weight substances and the like adhered around the wire electrode of the electrostatic adhesion method, and the discharge condition became uneven across the width of the electrode. Spots were also observed in the state of adhesion of the extruded melt to the rotating cooling roll. The thickness unevenness of the obtained biaxially stretched film was 16%.
Therefore, it was judged that long-term film formation was impossible.

Table 1 shows the above results.

[0042]

[Table 1] As shown in the results of Table 1, according to the present invention, by using an aliphatic polyester having a predetermined melt viscosity and melt-extrusion at a predetermined temperature, while preventing the occurrence of dirt,
By imparting a suitable viscosity to the extruded melt, an aliphatic polyester film having a uniform thickness can be obtained efficiently and continuously stably.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B29K 67:00 B29L 7:00 (72) Inventor Naonobu Oda 10-24 Toyocho, Tsuruga-shi, Fukui Prefecture Toyobo Co., Ltd.Tsuruga Branch Room (72) Inventor Tadashi Okuhira 2-1-1 Katata, Otsu-shi, Shiga F-term in Toyobo Co., Ltd. Research Laboratory (reference) 3E086 AD01 BA02 BA15 BB90 4F071 AA43 AA88 AF25 AH04 BB06 BB07 BC01 4F207 AA24 AG01 AH81 AR06 KA01 KA17 KK64 KK66 KL84 KM14 KW41 4J002 CF181 FD010 FD020 FD070 FD090 FD100 FD170 FD200 GG02

Claims (4)

[Claims] (1) a main repeating unit represented by the general formula -O-CH
While extruding a molten component mainly composed of an aliphatic polyester that is R-CO- (R represents H or an alkyl group having 1 to 3 carbon atoms), the extruded extruded melt is applied to a rotary cooling roll. In the method for producing an aliphatic polyester film, which has a process of obtaining an unstretched film by bringing the film into close contact and quenching while solidifying, the melt viscosity of the aliphatic polyester at 200 ° C. at a shear rate of 10 / sec is determined. , While using 1 × 10 ³ poise or more and less than 1 × 10 ⁶ poise,
The method for producing an aliphatic polyester film, wherein the melt extrusion is performed within a range of a melting temperature (Tm) of the aliphatic polyester to 250 ° C. 2. The method for producing an aliphatic polyester film according to claim 1, wherein the close contact with the rotary cooling roll is such that the extruded melt is charged and electrostatically adhered to the rotary cooling roll. 3. The method for producing an aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid. 4. The method for producing an aliphatic polyester film according to claim 1, further comprising a step of further stretching the unstretched film.